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Lyme disease may be carried to humans by the deer tick, but this time of year, it's not the deer who are playing host to this tiny insect. It's the Island's white-footed mice.

That's why scientists are so focused on the Vineyard mouse population. Teams from the University of Massachusetts Amherst and another from the Harvard School of Public Health are both trapping mice and drawing blood samples to test them for evidence of Lyme.

Depending on the time of year, upward of 90 per cent of the mice might test positive for Lyme antibodies, according to Sam Telford, a Harvard parasitologist who's been tracking Lyme disease both on the Vineyard and Nantucket for the last decade.

That might help explain why the Vineyard has the second highest incidence rate of Lyme disease in the state, second only to Nantucket. One in seven Island residents reports having had Lyme disease, according to a survey from the state Department of Public Health (DPH).

According to Dr. Dennis Hoak, infectious disease specialist from Edgartown, Island doctors are seeing more patients with Lyme symptoms this year, but there are no hard statistics to back that up.

What the experts do know is that mice could offer a key not only in forecasting Lyme cases but also in preventing transmission of the disease to humans.

With a grant from the federal Centers for Disease Control (CDC), two students from UMass this summer are field-testing a new device, a bait box that lures mice in and then coats them with a tick-killing chemical called fipronil, similar to the product that pet owners use on their dogs and cats.

"When the mouse goes back to its litter mates, it can pass the fipronil on to them as well, so it will kill the ticks on the rest of the mice in that litter," said Laura Blewett, a graduate student in wildlife conservation at UMass.

Ms. Blewett and her partner in the project, Molly Ellwood, have placed bait boxes on 50 residential sites around the Island, most of them in West Tisbury and Chilmark, where tick counts are known to be high.

To test the effectiveness of the bait boxes, the two students will drag for ticks in these areas over the summer and compare the numbers they collect, hoping to see a reduction in the deer tick population.

Similar studies are being conducted along the East Coast as far south as Maryland; if successful, they could lead to the development of a product that would be marketed and offered to the public by exterminators.

But Mr. Telford is a little skeptical about whether the bait-box approach will meet with any more consumer success than the Damminix tubes, which operated on a similar scientific principle. The tubes were also baited to attract mice and contained cotton balls soaked in another tick-killing chemical that would be brought back to the rest of the litter.

Damminix, he said, is no longer widely used not only because of its cost - several hundred dollars a year for one yard - but also because most of the ticks killed in this process are in the earliest larval stage. The real impact on Lyme-carrying ticks wouldn't be seen until the next year, said Mr. Telford.

While scientists lay bait boxes as one possible preventive measure, public health experts are focusing on increasing people's awareness of Lyme disease symptoms and the importance of daily tick checks.

Earlier last month, through another program enabled by the CDC grant, every permanent resident of the Island received a silver-colored pamphlet containing specific instructions on how to detect ticks.

"We want to increase people's confidence that they can perform a successful tick check," said Dr. Nancy Shadick, a rheumatologist and director of the Lyme Disease Center at Brigham and Women's Hospital in Boston.

The main message in the brochure is that while the deer ticks are indeed tiny, it is still possible to feel them and find them. A "tick-feel" card in the packet allows people to run their finger over raised dots approximating the sizes of both a nymph and adult tick.

The "tick dock card," presented in a pack, is laid out so that people can tape a tick on the paper and compare it to outline images of both deer ticks and dog ticks of both genders and various sizes. People can take the tick to their doctor to help determine what kind of tick bit them.

The big reason for spending time on a daily tick check is that it takes at least 24 hours for the tick to transmit bacteria to a human.

What makes the months of May, June and July the peak season for Lyme disease is that this tick is still in its nymphal stage, small as the point of a pen and hard to detect.

If that nymphal deer tick happens to have taken a "blood meal" from an infected mouse, then it's carrying Lyme bacteria and stands a chance of infecting a human if it stays burrowed in for more than a day.

More often than not, though, people don't think of Lyme disease until they are already suffering from symptoms - a rash that can be bull's-eye or doughnut-shaped coupled with flulike aches and fever. Swollen joints and facial paralysis can also occur.

The trick with getting hard data on Lyme cases is that most physicians now treat the symptoms prophylactically, prescribing antibiotics to treat the symptoms rather than waiting for a blood test to confirm the presence of Lyme antibodies.

The Vineyard is indeed a hotbed for Lyme and other illnesses passed on by the deer tick, including babesiosis and ehrlichiosis.

"The Vineyard is a very curious micro-environment where tick-borne diseases have clustered," said Dr. Hoak. "It's in the animals in the natural reservoir, and when people invade that environment, we're going to pick things up."

Mr. Telford is equally intrigued by the Island abundance of tick-borne illnesses. Last year, he joined the CDC study investigating the outbreak of pneumonic tularemia which began in the summer of 2000.

But he's also committed to finding out why Lyme disease thrives here. He's been trapping mice all over the Island and collecting all kinds of data from gender and age to Lyme antibodies.

Since last winter was so mild, Mr. Telford has observed, "We had mice breeding during the winter time. That means we probably have three times more mice than we usually do."

More mice could mean more ticks carrying the bacteria next year, he said. The bait boxes may have come just in time, but it's up to the scientists to analyze the data. Meanwhile, Dr. Shadick is urging regular tick checks, and Dr. Hoak is ready with the prescriptions for antibiotics.